This invention relates generally to turbomachinery, and specifically to rotary turbine and compressor components. In particular, the invention concerns counter-rotating turbomachinery for the turbine and compressor sections of a gas turbine engine.
Gas turbine engines (or combustion turbines) are built around a power core made up of a compressor, combustor and turbine, arranged in flow series with an upstream inlet and downstream exhaust. The compressor compresses air from the inlet, which is mixed which fuel in the combustor and ignited to generate hot combustion gas. The turbine extracts energy from the expanding combustion gas, and drives the compressor via a common shaft. Energy is delivered in the form of rotational energy in the shaft, reactive thrust from the exhaust, or both.
Gas turbine engines provide efficient, reliable power for a wide range of applications, including aviation, industrial power generation, and commercial heating and cooling. Small-scale engines such as auxiliary power units typically utilize a one-spool design, with co-rotating compressor and turbine sections. Larger-scale engines including jet engines and industrial gas turbines (IGTs) are generally arranged into a number of coaxially nested spools, which operate at different pressures and temperatures, and rotate at different speeds.
The individual compressor and turbine sections in each spool are subdivided into a number of stages, which are formed of alternating rows of rotor blade and stator vane airfoils. The airfoils are shaped to turn, accelerate and compress the working fluid flow, and to generate lift for conversion to rotational energy in the turbine.
Ground-based industrial gas turbines can be quite large, utilizing complex spooling systems for increased efficiency. Power is delivered via an output shaft connected to a mechanical load, such as an electrical generator, blower or pumping system. Industrial turbines can also be configured for combined-cycle operation, in which additional energy is extracted from the exhaust stream, for example in a low pressure steam turbine.
Aviation applications include turbojet, turbofan, turboprop and turboshaft engines. Turbojet engines are an older design, in which thrust is generated primarily from the exhaust. Modern fixed-wing aircraft typically employ turbofan and turboprop configurations, in which the low pressure spool is coupled to a propulsion fan or propeller. Turboshaft engines are used on helicopters and other rotary-wing aircraft.
Turbofan engines are commonly divided into high and low bypass designs. High-bypass turbofans generate most of their thrust via the fan, which drives airflow through a bypass duct oriented around the engine core. Low-bypass turbofans generate proportionally more power from the exhaust flow, delivering greater specific thrust but at some cost in noise and fuel efficiency, and are used on supersonic fighters and other high-performance aircraft. Unducted (open rotor) turbofans and ducted turboprops are also known, including counter-rotating and aft-mounted configurations.
Gas turbine engine performance depends on precise control of the working fluid flow, and on the relative loading of the various high and low pressure components. In particular, performance depends on efficient load transfer between rotor stages in the turbine and compressor sections, and on careful management of the axial flow velocity, including endwall contributions and the effects of relative Mach number on the performance of sequentially spaced rotor components in the compressor and turbine sections.